In an effort to further reduce motor vehicle emissions and improve air quality and public health, the United States Environmental Protection Agency has promulgated new rules that require lowering of sulfur content in gasoline beginning in 2017, and reduction of evaporative emissions from passenger cars, light-duty trucks, medium-duty passenger vehicles, and some heavy-duty vehicles (40 CFR parts 79, 80, 85 et al., titled “Control of Air Pollution from Motor Vehicles: Tier 3 Motor Vehicle Emission and Fuel Standards; Final Rule). Under the Tier 3 program, gasoline shall not contain more than 10 parts per million sulfur on an annual average basis by Jan. 1, 2017. This reduction is expected to reduce catalyst fouling and substantially improve the effectiveness of the vehicle emission control systems, leading to significant reductions in emissions of nitrogen oxides, volatile organic compounds, carbon monoxide, particulate matter, benzene, sulfur dioxide, 1,3-butadiene, formaldehyde, acetaldehyde, acrolein, and ethanol.
Under the Tier 3 standards, new specifications for the gasoline emissions test fuel used for testing highway vehicles have been adopted to better match the fuel that is currently being used. Specifically, in-use gasoline has changed considerably since the EPA last revised specifications for gasoline. Sulfur and benzene levels have been reduced, and gasoline containing 10 percent ethanol by volume has replaced non-oxygenated gasoline across the country. Section 1065.710(b) of Title 40 of the Code of Federal Regulations specifies test fuel properties for gasoline with ethanol (low-level blend only). The specification requires an Antiknock Index (R+M)/2 of 87.0-88.4, a sensitivity (R−M) of 7.5 (minimum), a Dry Vapor Pressure Equivalent (DVPE) in units of kPa of 60.0-63.4, 10% evaporation during distillation at 49-60° C., 50% evaporation during distillation at 88-99° C., 90% evaporation during distillation at 157-168° C., a final boiling point of 193-216° C., a post-distillation residue of 2.0 milliliters (maximum) of a 100 milliliter specimen (see ASTM D86), total aromatic hydrocarbons content of 21.0-25.0 volume present, C6 aromatics (benzene) content of 0.5-0.7 volume percent, C7 aromatics (toluene) content of 5.2-6.4 volume percent, C8 aromatics content of 5.2-6.4 volume percent, C9 aromatics content of 5.2-6.4 volume percent, C10 plus aromatics content of 4.4-5.6 volume percent, a total olefins content of 4.0-10.0 mass percent, an ethanol content of 9.6-10.0 volume percent (blended) or 9.4-10.2 volume percent (confirmatory), a total content of oxygenates other than ethanol of 0.1 volume percent (maximum), a sulfur content of 8.0-11.0 mg/kg, a lead content of 0.0026 g/liter (maximum), a phosphorus content of 0.0013 g/liter (maximum), copper corrosion of No. 1 Maximum per ASTM D130, a solvent-washed gum content of 3.0 mg/100 milliliters (maximum), and an oxidation stability of 1000 minutes (minimum) per ASTM D525. The ethanol (blended) specification is based on the volume percent ethanol content as determined during blending by the fuel supplier and as stated by the supplier at the time of fuel delivery (see 40 CFR 1065.710(b)(3)). The ethanol (confirmatory) specification refers to the volume percent ethanol content as determined analytically.
Section 1065.710 of Title 40 also specifies that the low-level ethanol-gasoline test fuel blend having nominally 10% ethanol (commonly called “E10 test fuel”) must be prepared from typical refinery gasoline blending component, and “may not use pure compounds, except as follows: (i) you may use neat ethanol as a blendstock, (ii) you may adjust the test fuel's vapor pressure by adding butane, (iii) you may adjust the test fuel's benzene content by adding benzene, and (iv) you may adjust the test fuel's sulfur content by adding sulfur compounds that are representative of those found with in-use fuels.”
It has been determined that it is extremely difficult to meet all of the antiknock, sensitivity, distillation, and compositional requirements of 40 USC §1065.710(b) using typical refinery gasoline blending components in combination with neat ethanol, butane, benzene and representative sulfur compounds. Generally, substantial trial and error is required to achieve all specifications concurrently. Further, once an appropriate blend has been determined, it is only usable for a relatively short period of time, since typical refinery gasoline blending components are constantly changing due to factors such as the source of the crude oil and seasonal adjustments to refinery operating parameters. It is most difficult to formulate an E10 test fuel within the specification having the required ranges for the various aromatic species while also meeting the total aromatic content and fuel distillation profile. Typical refinery gasoline blending components (or blendstocks) having a high aromatic content include heavy straight run (HSR) naphtha (petroleum), Aromatic 100 (a composition generally comprising a minimum of 98.0 volume percent aromatics and having a flashpoint of about 100 degrees Fahrenheit), Aromatic 150 (a composition generally comprising a minimum of 98.0 volume percent aromatics and having a flashpoint of about 150 degrees Fahrenheit), and Aromatic 200 (a composition generally comprising a minimum of 98.0 volume percent aromatics and having a flashpoint of about 200 degrees Fahrenheit). A problem with these aromatic refinery streams is that the composition can vary widely from batch to batch. Specifically, the distribution of C7, C8, C9 and C10+ aromatics can vary considerably from batch to batch, making it very difficult to formulate a finished test fuel meeting the very tight specifications of 40 CFR 1065.710(b). It is particularly difficult to formulate an E10 test fuel in accordance with 40 CFR 1065.710(b) that complies with the various aromatic species ranges while also meeting the total aromatic content requirement and fuel distillation profile.
It is highly desirable to develop a process for preparing E10 test fuels in accordance with 40 CFR 1065.710(b) without employing a trial and error process typically requiring several iterative failures before meeting all specifications.